The presence of hydrogen sulfide (H2S) in the course of manufacturing chemical materials from coal or petroleum will poison and thus deactivate catalysts used in the subsequent processing stages. A large amount of industrial waste water or waste gases also contain considerable hydrogen sulfide (H2S) and other sulfides, which will pollute the environment or poison humans or animals if directly emitted. Presently, desulfurizer are usually used in the desulfurization of hydrogen sulfide (H2S)-containing gases such as coal gas, hydrogen, synthetic gas, ammonia gas and gaseous hydrocarbon etc., or hydrogen sulfide-containing liquid hydrocarbons, such as kerosene, gasoline and cyclohexane etc. There are many kinds of desulfurizers, and iron oxide is one conventional desulfurizer. The disadvantages of this kind of desulfurizers are that they can be applied to a narrow range of temperature and air velocity, have a low reactive efficiency and sulfur capacity, and generally can only be employed in the primary crude desulfurization or in combination with other kinds of desulfurizers.
At present, the active components of most iron oxide desulfurizers include other metal oxides besides iron oxides. For example, Chinese Patent Application-CN1287875A discloses a composition MxOy.Fe2O3.nH2O comprising ferric oxide monohydrate and one or more other metal compounds, wherein the metal is selected from the group consisting of Ti, Co, Ni, Mo, Zn, Cd, Cr, Hg, Cu, Ag, Sn, Pb and Bi, and/or alkaline-earth metals such as Ca, Mg. Chinese Patent Application-CN1121950A discloses a desulfurizer with crude iron ore, scoria and zinc oxide serving as raw material. Chinese Patent Application-CN1068356A discloses a desulfurizer with iron-mud waste, sintered zinc ferrite as raw material. There are also desulfurizers using crude iron-containing minerals as raw material. For example, Chinese Patent Application-CN1121950A discloses a desulfurizer comprising crude iron ore, scoria and zinc oxide, and Chinese Patent Application-CN1368537A discloses a desulfurizer comprising ore rich in iron, lignite and a small quantity of calcareousness, wherein the ore rich in iron can be hematite. Japanese Patent Application No. JP59039345 discloses a desulfurizer comprising 40 to 90% iron oxide (such as hematite), titanium dioxide and silicon dioxide. Although the costs of said desulfurizer are low, it is difficult to keep the active components of the desulfurizer stable because the components of the raw material are variable.
Additionally, ferrite is used as the raw material to prepare desulfurizers with a wet method. For example, Chinese Patent Application-CN1312132A discloses a desulfurizer prepared by reacting ferrous sulphate solution, ammonia as precipitator, calcareousness, sodium carbonate, and a small quantity of metal oxides. Several side-reactions will take place during the precipitation when the ferric salt solution precipitation method is used to form the iron oxides, and it is difficult to control these side-reactions by adjusting the pH value. Thus, it is difficult to control the final composition of the active components, which makes the sulfur capacity uncontrollable.
Additionally, there are also a kind of desulfurizers containing iron or iron oxide as sole active component. For example, Chinese Patent Application-CN1539545 discloses a desulfurizer comprising 15 to 80% iron oxide and Direct Reduced Iron (spongy iron); U.S. Pat. No. 5,102,636 discloses a desulfurizer comprising 5 to 95% iron oxide and 95 to 5% iron complex. This kind of desulfurizers sufficiently take advantage of the desulfurizing function of the iron, however, the cost is relatively high.
Chinese Patent Application-CN 1395994A discloses a process for preparing an iron additive used in iron-alkali desulfurizing catalyst, wherein a ferrous sulfate (or ferrous chloride) solution and a sodium carbonate (or sodium hydroxide) solution are mixed to cause precipitation reaction to form said iron additive. This reaction in the solution is apt to obtaining colloid which is uneasy to be washed.
It is well known that the performance of a desulfurizer primarily depends on factors, such as sulfur capacity, desulfurizing precision and temperature. The higher the sulfur capacity and the desulfurizing precision, the better the performance of the desulfurizer becomes. However, the sulfur capacity of the present iron oxide desulfurizers is less than 40%.